Although cell-based wireless communication systems first attracted the attention of the average consumer as a useful mechanism for communicating voice signals, modem cellular systems today are often used to transport digital data. The explosive growth in both business and personal transmission of digital data via cellular systems has resulted in the deployment of multiple wireless data transport technologies (WDTs). WDTs includes Cellular Digital Packet Data (CDPD), overhead control channel data transport communications, and Short Message Service (SMS), as implemented by IS-136, IS-91(A), IS-95, IS-637, and GSM-compatible cellular systems.
CDPD is a digital cell-based network that is deployed in cellular telephony networks as an overlay network to an existing circuit-switched cellular system. CDPD provides a way to transmit data over an analog cellular telephone network and is best-suited for applications requiring short, bursty, data transmissions. For example, data is transmitted in packets of information, rather than in a continuous data stream, and occupies naturally occurring lulls or gaps in the usage of the cellular communication channels. Each data packet has an address using the Internet Protocol (IP). Data packets can be transmitted across the cellular network independently, with the network protocols managing access, routing, and prioritization of packet distribution. The CDPD technology is described in U.S. Pat. No. 5,819,184, which is hereby incorporated fully herein by reference.
Although CDPD supports small and medium volume data communications, CDPD at present lacks adequate coverage for some data communication applications because selected cellular carriers have not elected to deploy CDPD technology in their service areas. CDPD is at present typically deployed only in dense urban areas and is not available in all geographical areas that might benefit from this WDT.
The “CELLEMETRY” data communications service, as described in U.S. Pat. No. 5,546,444, takes advantage of the underutilized capacity of the overhead control channels of advanced mobile phone service (AMPS) and digital AMPS-based (DAMPS) cellular telephony systems to convey short data messages between a subscriber unit and a base station. Although the overhead control channels are primarily used to transmit necessary information for all incoming and outgoing call initiations, this overhead control channel data transport service also can insert data content within an Autonomous Registration signal or a Call Origination signal to convey that data content. The “CELLEMETRY” data communications service can wirelessly convey data content from a subscriber unit to a remote host via the cellular switch by mimicking the conventional roaming (or Call Origination) messages of the AMPS/DAMPS overhead control channels and the SS7/IS-41 network. Detailed information describing the “CELLEMETRY” data communications service can be found in U.S. Pat. No. 5,546,444, which is fully incorporated herein by reference. An alternative overhead control channel data transport service is based on the use of a feature request field in a AMPS/DAMPS message, as described in U.S. Pat. No. 5,771,455.
Because the “CELLEMETRY” and the feature request-based data communications services rely upon the overhead control channel as the data transport medium, these communication services can lack sufficient data carriage capacity for certain applications requiring expanded data content, particularly in the direction toward the subscriber unit. Consequently, the “CELLEMETRY” and feature request-based data communications services typically are not able to support wireless data communication applications requiring the communication of expanded data content or high volume communications.
In view of the foregoing, there is a need in the art for a data communications system that can overcome the limited deployment of CDPD networks and the limited data capacity of overhead control channel data transport technologies, such as the “CELLEMETRY” data communications service. There is a further need in the art for a data communications device that is compatible with multiple wireless data transmission technologies to support consistent and economical cell-based communication operations based upon the most appropriate WDT technology that is available in the service location. The present invention solves the problems of the prior art by providing a communications device that can support multiple WDT technologies, including CDPD, control channel data transport technologies, such as the “CELLEMETRY” data communications service, and other WDT technologies, such as voice-channel modem technologies. For example, a communications device constructed in accordance with the present invention can select the appropriate WDT technology based upon the transport technology best suited to accomplish the communication objective.